Field of the Invention
The present invention relates to a method for producing a composition for forming a coating film for a lithography used in microfabrication in manufacture of semiconductor devices and the like, especially for producing a composition for forming a resist upper layer film, a composition for forming a silicon-containing resist under layer film, and a composition for forming an organic under layer film which are used in a multilayer resist method.
Description of the Related Art
As the LSI becomes highly integrated and achieves high-speed processing, the pattern size has been miniaturized rapidly. In relation to such miniaturization, lithography technologies accomplish fine patterning by adopting light sources with shorter wavelength and correspondingly selecting adequate compositions for forming a coating film for a lithography.
In miniaturization by using the same light source, however, if the pattern width is reduced with the thickness of the photoresist film unchanged, the aspect ratio of the developed photoresist pattern increases, resulting in a collapse of the pattern. Accordingly, the thickness of the photoresist film has been reduced in accordance with the progress of photoresist pattern miniaturization in order to keep the aspect ratio of the photoresist pattern within a proper range. As the reduction of the film thickness of the photoresist film proceeds, there arises another problem of lowering an accuracy of pattern transfer to a body to be processed.
The multilayer resist method is one of the methods to solve such a problem. In this method: an under layer film having a different etching selectivity from that of the photoresist film (resist upper layer film) intervenes between the resist upper layer film and the substrate to be processed; a pattern is formed in the resist upper layer film, and the pattern is transferred to the under layer film by dry etching, using the resist upper layer film pattern as a dry etching mask; and this pattern is further transferred to the substrate to be processed by dry etching, using the under layer film as a dry etching mask.
These compositions for forming a coating film for a lithography used in such multilayer resist methods, for example, a resist upper layer film, a silicon-containing resist under layer film, an organic under layer film usually contain metal impurities due to an environment, a device, an equipment, and raw materials. In a multilayer resist process, pattern transfers by dry etching are repeated, and accordingly such a metal impurity acts as an etching mask under certain dry etching conditions and is transferred to a substrate to be processed for a semiconductor device. This induces an electrical fault such as an open fault and a short fault in a circuit when producing a semiconductor device, and causes lowering of a production yield of a semiconductor device.
At present, purification of raw materials is considered to be most effective in order to prevent a failure caused by the metal impurity. For example, Patent Document 1 discloses a method to purify a raw material polymer by contacting with aqueous acid solution. In a composition for forming a coating film for a lithography used in the cutting edge process, however, it is impossible to totally remove an etching defect only by purification of a polymer, and it has been required to reduce the defects furthermore.